Glenda has been over charged by $3.40 for her purchase. Below is the solution: First you have to multiply the prices for frames and mats by number of pieces: 5.89 x 4 = 23.56 12.95 x 4 = 51.80 Then add amount: 23.56 + 51.80 = 75.36 Then multiply by 6.5% $75.36 * 6.5% = $4.90 $75.36 + $4.90 = $80.26 $80.26 + $8.20 = $88.46 $91.86- $88.46 = $3.40